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What's the difference between PET, PP and PE ?

May. 28, 2019

Polyethylene Terephthalate, chemical formula is -OCH2-CH2OCOC6H4CO- , referred to as PET, is a high polymer, which is derived from the dehydration condensation reaction of ethylene terephthalate. Ethylene terephthalate is obtained by esterification of terephthalic acid and ethylene glycol. PET is a milky white or light yellow, highly crystalline polymer with a smooth, shiny surface. Excellent physical and mechanical properties in a wide temperature range, long-term use temperature up to 120 °C, excellent electrical insulation, even at high temperature and high frequency, its electrical performance is still good, but poor corona resistance, anti-corrosion Creep resistance, fatigue resistance, abrasion resistance, and dimensional stability are all good. 


1. Good mechanical properties, impact strength is 3 to 5 times that of other films, and good folding resistance.

2. Oil resistant, fat resistant, dilute acid, dilute alkali, resistant to most solvents.

3. It has excellent high and low temperature resistance, can be used for a long time in the temperature range of 120 °C, can withstand high temperature of 150 °C for short-term use, can withstand low temperature of -70 °C, and has little effect on mechanical properties at high and low temperatures.

4. Gas and water vapor permeability is low, both excellent gas barrier, water, oil and odor properties.

5. High transparency, can block ultraviolet rays, good gloss.

6. Non-toxic, odorless, good health and safety, can be directly used for food packaging.

PP is the abbreviation of Polypropylene. PP (polypropylene) is prepared by catalytic polymerization of a propylene monomer using a Ziegler-Natta catalyst, and is a crystalline isotactic polymer in which molecular chain links are well aligned. PP (polypropylene) can be divided into isotactic PP (polypropylene) and random PP (polypropylene) according to its crystallinity. Isotactic polypropylene is a highly crystalline thermoplastic resin with crystallinity of over 95% and molecular weight of 8- Between 150,000; atactic polypropylene is a non-crystalline, slightly viscous white wax at room temperature, low molecular weight, 3000-10000, structural irregularities lack cohesion, less application. A commonly used PP material is isotactic polypropylene. Polypropylene is a high polymer. The monomer is propylene CH2=CH-CH3. Polypropylene is obtained by polyaddition of polypropylene. The chemical formula can be expressed as (C3H6)n, and the structure can be expressed as [-CH2-CH ( CH3)-]n. English full name: Polypropylene. The molecular structure of PP is a typical bulk structure, which is a crystalline polymer.


Automotive industry (mainly using PP with metal additives: fenders, ventilation pipes, fans, etc.), instruments (dishwasher door liners, dryer vents, washing machine frames and covers, refrigerator door liners, etc.) , consumer goods (turf and garden equipment such as lawn mowers and sprinklers, etc.).

Chemical and physical properties:

PP is a semi-crystalline material. It is harder and has a higher melting point than PE. Since PP products of homopolymer type are very brittle when the PP temperature is higher than 0 °C, many commercial PP materials are random copolymers of 1 to 4% ethylene or block copolymers of higher ethylene content. The copolymer type PP material has a low heat distortion temperature (100 ° C), low transparency, low gloss, low rigidity, but has a stronger impact strength. The strength of PP increases as the ethylene content increases. The Vicat softening temperature of PP is 150 °C. Due to the high degree of crystallinity, this material has excellent surface stiffness and scratch resistance. There is no environmental stress cracking problem in PP.Typically, PP is modified by the addition of glass fibers, metal additives or thermoplastic rubber. The flow rate of PP has a MFR ranging from 1 to 40. Low MFR PP materials have better impact resistance but lower elongation. For materials of the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, generally 1.8 to 2.5%. And the direction uniformity of shrinkage is much better than materials such as PE-HD. The addition of 30% glass additive can reduce the shrinkage to 0.7%. Both the homopolymer type and the copolymer type PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance, and solubility resistance. However, it is not resistant to aromatic hydrocarbons such as benzene solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents, and the like. PP does not have oxidation resistance at high temperatures like PE. Polypropylene (PP) is one of the lighter plastics, and it has excellent electrical properties and can be used as a moisture-resistant high-frequency insulation material. PP is a crystalline polymer which exhibits a large shrinkage (1.0%-1.5%) due to a large change in specific volume and a high degree of molecular orientation when the melt is condensed. In the molten state of PP, the effect of lowering the viscosity by heating is not significant. Therefore, in the molding process, the injection pressure and shear rate should be increased to improve the molding quality of the product.

Polyethylene, abbreviated as PE, is a thermoplastic resin obtained by polymerization of ethylene. Industrially, copolymers of ethylene and a small amount of an α-olefin are also included. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (minimum use temperature can reach -70~-100°C), good chemical stability, and can resist most acid and alkali corrosion (not resistant to oxidizing properties) Acid), insoluble in general solvent at normal temperature, low water absorption, excellent electrical insulation properties, polyethylene characteristics, odorless, non-toxic, hand-like wax, excellent low temperature resistance (minimum use temperature up to -70~- 100 ° C), good chemical stability, can withstand most of the acid and alkali erosion (not resistant to acid with oxidizing properties), insoluble in common solvents at room temperature, low water absorption, but because it is a linear molecule can be slowly soluble in some organic Solvent, and does not swell, and has excellent electrical insulation properties; however, polyethylene is very sensitive to environmental stress (chemical and mechanical action) and has poor heat aging resistance. The nature of polyethylene varies from species to species and depends primarily on molecular structure and density.


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